Improving ZTF Photometric Calibration

Summary and Comment

ZTF photometry clearly exhibits many systematic effects that are caused by a variety of different sources. We have used millions of ZTF objects matched to PS1 to derive corrections for these systematics. These effects include the magnitude bias, the residual spatial structure of the photometry, and residual field offsets.

The additional ZTF photometric systematics that increase the scatter measured between individual photometry points are yet to be addressed. These are largely dependent on how the photometry software responds to varying observing conditions. In particular, the sky level, the seeing and airmass. The problems (observation condition dependent systematics) are most evident in fields with < 3000 calibrator stars.